Decadal Changes of Meridional Eddy Heat Transport in the Subpolar North Atlantic Derived From Satellite and In Situ Observations

The interannual variability of the meridional eddy heat transport in the North Atlantic is investigated based on the combined use of satellite observations of sea level anomaly (SLA) and sea surface temperature (SST) over the 25 year period from 1993 to 2017. The focus is on 47 degrees N, a latitude close to the boundary between the subpolar and the subtropical gyres. The vertical structure of the eddy heat transport is reconstructed in 10 degrees longitude x 5 degrees latitude boxes from a composite analysis of Argo profile data and observations of mesoscale eddies in altimetric SLA. The transport is surface intensified with almost 95% happening above the pycnocline. It can vary immensely both zonally and vertically, in some cases reversing sign below the pycnocline. The basin-wide integrated eddy heat transport accounts for around 6% of the total meridional heat transport. During the observed period, the eddy heat transport increased on average by 0.6 TW/yr, accelerating to 1.3 TW/yr after 2005. The observed trends and variations in the eddy heat transport can be related to the large-scale temperature gradients in the region and in response to the North Atlantic Oscillation. They provide a considerable contribution to the variability of the total oceanic heat transport, suggesting a potentially important forcing mechanism in the ocean component of the climate system. Key Points Eddy heat transport across 47 degrees N in the subpolar North Atlantic is estimated from satellite altimetry, SST, and Argo profile data Eddy heat transport across 47 degrees N accounts for 6% of the total observed meridional heat transport Time variability and trends in the eddy heat transport account up to one third of the mean